1. Field of the Invention
This invention generally relates to surface acoustic wave devices that may be used for a television (simply referred to as TV, hereinafter), a video tape recorder (simply referred to as VTR, hereinafter), a DVD (Digital Versatile Disk) recorder, and a filter element and an oscillator or the like of a portable phone or the like, and a method for manufacturing thereof.
2. Description of the Related Art
A surface acoustic wave device (simply referred to as SAW device, hereinafter) is widely used for various circuits that process radio signals in the frequency range of 45 MHz to 2 GHz. Examples of those circuits are a bandpass filter for transmission, a bandpass filter for reception, a resonator for local oscillator, an antenna duplexer, an intermediate frequency filter and an FM modulator.
The signal processing devices are now miniaturized, and there is an increasing demand for downsizing of electronic components such as SAW devices. In particular, portable electronic devices such as portable phones require surface-mounting, height-lowered SAW devices.
Recently, there has been a proposal for fabricating SAW devices of surface mounting type. This proposal may be applied to other types of electronic components. The proposed method employs a sheet-like package substrate, on which electronic elements like SAW device chips are mounted in an array of rows and columns at intervals. The electronic elements are electrically connected to the package substrate and are then sealed with caps. Finally, the package substrate is cut and divided into individual electronic components.
Japanese Patent Application Publication No. 59-010015 (hereinafter referred to as Document 1) discloses a method of fabricating piezoelectric devices. In this method, piezoelectric vibrator elements are arranged in rows and columns at intervals on a ceramic substrate having a sheet shape. Caps are adhered to the ceramic substrate so as to cover the piezoelectric vibrator elements. Then, the ceramic substrate is cut along laser slits provided on the ceramic substrate, and is divided into individual piezoelectric vibrators.
The ceramic caps separately cover the piezoelectric vibrator elements. The ceramic caps are coated with adhesive like epoxy and are adhered to the piezoelectric vibrator elements on the ceramic substrate, so that the element can be hermetically sealed.
However, adjacent caps pull each other or the vibrator element and the cap pull each other due to the surface tension of the adhesive agent until the hardening of the adhesive is completed after the caps are mounted on the ceramic substrate. Thus, the caps may be displaced. The displacement of caps may cause a difficulty in cutting the ceramic substrate and may result in piezoelectric vibrators having an uneven outer shape. The above problem will now be described in more detail by referring to a manufacturing process of a conventional SAW device.
FIGS. 12A through 12E illustrate a manufacturing process of a conventional SAW device. As shown in FIG. 12A, SAW device elements 110 are mounted, in an array of rows and columns at intervals, on a resin substrate 120 having metal patterns formed on both surfaces thereof by an element transfer tool 111.
Next, as shown in FIG. 12B, the SAW device elements 110 and the resin substrate 120 are connected to each other through metal wires 112 by a bonding capillary 113.
Then, as shown in FIG. 12C, resin caps 130 are mounted on the resin substrate 120 so as to cover the SAW device elements 110, and are then adhered to the resin substrate 120 through an adhesive.
Thereafter, as shown in FIG. 12D, the resin substrate 120 is cut along spaces between the resin caps 130 by a dicing blade 141. Then, as shown in FIG. 12E, SAW devices 101 are picked up one by one by a transfer tool 142.
FIGS. 13A and 13B illustrate a displacement of the resin cap 130 caused by the surface tension of the adhesive agent. As shown in FIG. 13A, the resin caps 130 are adhered to the resin substrate 120 through an adhesive 131. In this case, the surface tension of the adhesive 131 displaces the resin cap 130 along an arrow X, when the adjacent adhesive 131 connect to each other. Thus, the resin cap 130 deviates from the mounted position.
In addition, as shown in FIG. 13B, the adhesive 131 sometimes flows into the resin cap 130 and is in touch with the SAW device element 110. In this case, the resin cap 130 is horizontally pulled toward the SAW device element 110 along an arrow Y caused by the surface tension of the adhesive 131. Thus, the resin cap 130 deviates from the mounted position.
FIGS. 14A and 14B illustrate a cutting surface of the SAW device 101. More specifically, FIG. 14A is a cross-sectional view of SAW devices 101 before cutting, and FIG. 14B is a cross-sectional view of SAW devices 101 after cutting.
As shown in FIG. 14B, the adhesive 131 and the resin substrate 120 having metal patterns 121 and 122 formed on both surfaces thereof have a common cutting face after being cut by the dicing blade. In this case, the adhesive 131 and the end parts of the resin substrate 120 located outside of the resin cap 130 are unused areas formed on the side of the SAW device 101 caused by the method of manufacturing above. The unused areas make it difficult to miniaturize the SAW device 101. In addition, the SAW devices 101 after cutting may have unused areas different in size and shape caused by the displacement of the resin cap 130 and so on. Therefore, the conventional SAW devices have unstable outer shapes.